An antenna used in a base station including a repeater of a radio communication system may have various shapes and structures, and in recent years, radio communication antennas generally have used a dual polarization antenna structure by applying a polarization diversity scheme.
The dual polarization antenna generally has a structure in which radiation elements, for example, in the form of four dipoles are appropriately arranged on at least one reflective plate that stands in the lengthwise direction thereof, in the form of a tetragonal shape or a rhombus shape. For example, those of the four radiation elements which are located in a diagonal direction are paired, and each of the radiation element pairs are used to transmit (or receive) one corresponding linear polarization of the two orthogonal linear polarizations, for example, arranged at +45 degrees and −45 degrees with respect to a vertical (or horizontal line).
An example of such a dual polarization antenna is disclosed in Korean Patent Application No. 2000-7010785 first filed by Kathrein-Verke Kage (entitled ‘Dual polarization multi-band antenna’).
Meanwhile, the horizontal beam width of a radio communication antenna generated by each radiation element (and a combination of radiation elements) is one of the very important characteristics of the corresponding antenna, and steady studies on the design of a radiating element and an entire antenna have been conducted to satisfy a beam width required for service conditions and environments. Then, studies for making beam width as wide as possible have been made in order to allow the corresponding antenna to have a wider coverage, and studies for making beam width as narrow as possible have been made to allow the corresponding antenna to have a narrower coverage.
It is preferable to apply a radio communication antenna having excellent side lobe characteristics as well as a narrow beam width to a base station (for example, a small-scale or ultra-small base station/repeater) that may be installed when many subscribers are concentrated on a specific area, such as a stadium or a large scale auditorium. That is, when many subscribers are concentrated on a specific area, a radio communication antenna is designed to have a narrow beam width in consideration of a capacity that may be processed by the corresponding base station/repeater. Furthermore, a business person densely installs base stations/repeaters having radio communication antennas with a narrow beam width in a corresponding area to secure processing capacity for many subscribers.
FIG. 1 is a plan view of a general radio communication antenna having a narrow beam width, in which four radiation modules 11, 12, 13, and 14 that generate an X polarization, respectively are installed on one reflective plate 10 in a rectangular arrangement structure. The radio communication antenna having a narrow beam width forms one radiation beam (having a narrow beam width) by combining the radiation beams of the four radiation modules 11, 12, 13, and 14. Then, the interval between the four radiation modules 11, 12, 13, and 14 is precisely set so that the radiation beams of the four radiation modules 11, 12, 13, and 14 are appropriately combined. The narrow beam width is generally set by providing a constant distance between the radiation modules in consideration of processed frequencies, and the distance between the radiation modules should be longer in order to obtain a narrower beam width.
However, because a radio communication antenna having a narrow beam width is generally applied to a small-scale or ultra-small base station/repeater, the size of an antenna may be a big burden when the corresponding antenna is designed using four radiation modules 11, 12, 13, and 14. Accordingly, a need for a radio communication antenna having a narrow beam width while having a small size is urgently required.